'Alien' Argentine Ants May Have Met Their Match

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Argentine ants (Linepithema humile) are among the most
aggressive invasive insects in the United States. But after
pushing out native ant species in local ecosystems across the
country, the little conquerers may have finally met their match.

Asian needle ants have already been found from Alabama to New
York City to Oregon, and their venomous stings can cause allergic
reactions in some humans.

While studying a supercolony of Argentine ants in North Carolina,
researcher Eleanor Spicer Rice, then a doctoral student at North
Carolina State University, spotted some Asian needle ants — a
strange sight, as Argentine ants usually attack other ants in
their territory. To investigate further, Spicer Rice and Jules
Silverman, a professor of entomology at NC State, studied how the
two species were spread across a 116-acre (47-hectare) office
park in Morrisville, N.C. [ Gallery:
Stunning Photos of the World's Ants ]

In 2008, they found Argentine ants in 99 percent of the sample
sites within the study area, while Asian needle ants were found
in just 9 percent of the sites. By 2011, the Argentine ants'
reach dropped to 67 percent of the sample sites, while the Asian
needle ants had expanded their territory to 32 percent of the
sites. The two species shared 15 percent of the sample points,
the researcher said.

"This is the first time we've seen another ant species take
territory from Argentine ants," Spicer Rice said in a statement.
She explained that Asian needle ants might have an edge, because
they start reproducing earlier in the spring while Argentine ants
remain quite dormant until late April or May.

"The Asian needle ant is moving into forests and urban
environments at the same time. And because it is active at cooler
temperatures, it could move into a very broad range of
territory," Spicer Rice said.

The researchers say it's not known how Asian needle ants displace
other ant species, but their spread could have negative
consequences for local ecosystems, especially if they push out
native ant populations that play a crucial role in dispersing
plant seeds.

The research was detailed online Feb. 8 in the journal
PLOS ONE. The team is now studying why Argentine ants are not
fighting back against Asian needle ants, according to a statement
from NC State.

Argentine ants have invaded, only to retreat in other parts
of the world. They once posed a multi-million dollar pest-control
problem in New Zealand, but researchers in 2011 found that huge
colonies of the ants had disappeared, possibly because inbreeding
may have left them vulnerable to disease.